Object reconstruction from dense light fields via depth from gradients

ABSTRACT

The present disclosure relates to techniques for reconstructing an object in three dimensions that is captured in a set of two-dimensional images. The object is reconstructed in three dimensions by computing depth values for edges of the object in the set of two-dimensional images. The set of two-dimensional images may be samples of a light field surrounding the object. The depth values may be computed by exploiting local gradient information in the set of two-dimensional images. After computing the depth values for the edges, depth values between the edges may be determined by identifying types of the edges (e.g., a texture edge, a silhouette edge, or other type of edge). Then, the depth values from the set of two-dimensional images may be aggregated in a three-dimensional space using a voting scheme, allowing the reconstruction of the object in three dimensions.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/421,178, filed Nov. 11, 2016, the entire disclosure of which ishereby incorporated by reference.

BACKGROUND

Reconstructing objects in three dimensions from a set of two-dimensionalimages is a long standing problem in computer vision. And despitesignificant research efforts, objects with thin features still poseproblems for many reasons. First, the thin features occupy only a smallnumber of pixels in the views that they are visible in, making locatingthem difficult. Moreover, many object reconstruction techniques miss thethin features because the techniques require patches on the objects tobe several pixels wide, which is not always the case with thin features.The thin features are also usually only visible in a small number ofviews, making matching the thin features between different viewsdifficult. Other reconstruction techniques face difficulties withtexture-less thin features because it is hard for such techniques tolocalize the features using photoconsistency values inside a volumetricdiscretization, often resulting in elimination of these features in thereconstruction. Therefore, there is a need in the art to improvetechniques for reconstructing objects in three dimensions from a set oftwo-dimensional images.

SUMMARY

The present disclosure relates generally to object reconstruction. Moreparticularly, techniques are described for reconstructing an object inthree dimensions that is captured in a set of two-dimensional images.

In some embodiments, the object is reconstructed in three dimensions bycomputing depth values for edges of the object in the set oftwo-dimensional images. In such embodiments, the set of two-dimensionalimages may be samples of a light field surrounding the object. The depthvalues may be computed by exploiting local gradient information in theset of two-dimensional images, allowing the depth values for differentedges to be computed in parallel. After computing the depth values forthe edges, depth values between the edges may be determined byidentifying types of the edges (e.g., a texture edge, a silhouette edge,or other type of edge). Then, the depth values from the set oftwo-dimensional images may be aggregated in a three-dimensional spaceusing a voting scheme, allowing the reconstruction of the object inthree dimensions.

Various embodiments are described herein, including methods, systems,non-transitory computer-readable storage media storing programs, code,or instructions executable by one or more processors, and the like. Forexample, a method may include receiving a light field represented bymultiple images, including at least a first image and a second image.The multiple images may capture an object at different viewpoints. Forexample, the first image may be at a different viewpoint than the secondimage. In some embodiments, the light field may be unstructured.

The method may further perform the following steps for each point of theobject located on an edge of the object in the first image, the stepsincluding identifying a first point of the object in the first image.The first point may be an edge of the object from the viewpoint of thefirst image. Based on the first point, a second line may be identifiedin the second image, the second line having a direction of an epipolarline for the first point of the object in the first image.

The steps may further include identifying one or more second pointsalong the second line. Based on projecting the one or more secondpoints, one or more additional first points may be identified along afirst line, the first line intersecting the first point.

A second point of the one or more second points may be determined tocorrespond to a first point of the one or more first points based on acolor of each of the one or more first points and a color of each of theone or more second points. The correspondence between the second pointand the first point indicates that the second point is an estimate ofwhere the first point is in the second image. In response to determiningthat the second point corresponds to the first point, a depth may becomputed for the first point based on the first point and the secondpoint. In some embodiments, the depth may be computed using a colorgradient for the first image, the color gradient based on colors of theone or more first points and the one or more second points. For example,a direction of the color gradient may be used to estimate the depth.

In some embodiments, the depth for an edge may be propagated to one ormore points around the edge based on a type of the edge. For example,when the edge is determined to be a texture, the depth for the edge ispropagated on both sides of the edge (i.e., in two dimensions). When theedge is determined to be a silhouette, the depth for the edge ispropagated on one side of the edge (i.e., in one dimension).

One method for determining the type of the edge is to identify multiplepoints along a first line perpendicular to the edge in a first image,identify the edge in a second image, identify multiple points along asecond line perpendicular to the edge in the second image, and determinethe type of the edge based on a color of each of the one or more pointsalong the first line and each of the one or more points along the secondline. In the method for determining the type of the edge describedabove, the multiple points along the first line may be a first imagegradient, and the multiple points along the second line may be a secondimage gradient. In addition, a first point of the multiple points alongthe first line may be on a particular side of the edge in the firstimage and a second point of the multiple points along the second linemay be on the particular side of the color edge in the second image. Insuch examples, the edge is a first type when the first point and thethird point are different colors and the edge is a second type when thefirst point and third point are the same color.

After the above steps are performed for each point of the object locatedon an edge in the first image, a depth map may be generated for thefirst image using the computed depths. Additionally, similar steps maybe performed for each image of the multiple images such that multipledepth maps are generated. Using the multiple depth maps, a mesh for theobject may be generated, where each point of the object is determined bycomparing depths of the point across the multiple depth maps. The meshbe a three-dimensional representation of the one or more objects. Insome embodiments, the mesh may be rendered such that a user may view themesh.

This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used in isolationto determine the scope of the claimed subject matter. The subject mattershould be understood by reference to appropriate portions of the entirespecification of this patent, any or all drawings, and each claim.

The foregoing, together with other features and embodiments, will bedescribed in more detail below in the following specification, claims,and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures:

FIG. 1 is a diagram depicting stages for generating a mesh for an objectaccording to certain embodiments;

FIG. 2 is a simplified flowchart depicting processing performed forgenerating a mesh for an object according to certain embodiments;

FIG. 3 is a simplified flowchart depicting processing performed fordetermining a depth of a point on an object according to certainembodiments;

FIG. 4 is a diagram depicting a depth of a point on an object beingdetermined;

FIGS. 5A-5D illustrate an example for determining corresponding pointsof an object between images;

FIG. 6 is a simplified flowchart depicting processing performed foridentifying a type of an edge of an object;

FIG. 7 is an image where edges may be identified;

FIGS. 8A and 8B are portions of multiple images that are used todetermine a type of an edge;

FIG. 9A is an image illustrating only silhouette edges

FIG. 9B is an image illustrating only texture edges;

FIG. 10 is a simplified flowchart depicting processing performed forobject reconstruction using a particular depth detection technique;

FIG. 11 is a simplified flowchart depicting processing performed forobject reconstruction using a particular propagation technique; and

FIG. 12 illustrates an example of a computer system.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofembodiments of the present disclosure. However, it will be apparent thatvarious embodiments may be practiced without these specific details. Thefigures and description are not intended to be restrictive.

The ensuing description provides exemplary embodiments only, and is notintended to limit the scope, applicability, or configuration of thedisclosure. Rather, the ensuing description of the exemplary embodimentswill provide those skilled in the art with an enabling description forimplementing an exemplary embodiment. It should be understood thatvarious changes may be made in the function and arrangement of elementswithout departing from the spirit and scope of the present disclosure asset forth in the appended claims.

Reconstructing objects in three dimensions from a set of two-dimensionalimages is a longstanding problem in computer vision. And despitesignificant research efforts, objects with thin features still poseproblems for many reasons. For example, the thin features occupy only asmall number of pixels in the views that they are visible in, makinglocating them difficult. The thin features are also usually only visiblein a small number of views, making matching the thin features betweendifferent views difficult.

In some embodiments, an object is reconstructed in three dimensions bycomputing depth values for edges of the object in the set oftwo-dimensional images. In such embodiments, the set of two-dimensionalimages may be samples of a light field surrounding the object. The depthvalues may be computed by exploiting local gradient information in theset of two-dimensional images, allowing the depth values for differentedges to be computed in parallel. After computing the depth values forthe edges, depth values between the edges may be determined byidentifying types of the edges (e.g., a texture edge, a silhouette edge,or other type of edge). Then, the depth values from the two-dimensionalimages may be aggregated in a three-dimensional space using a votingscheme, allowing the reconstruction of the object in three dimensions.

FIG. 1 is a diagram depicting stages for generating a mesh for an objectaccording to certain embodiments. The stages may begin at an input stage110 when multiple images are received. The multiple images may capture alight field surrounding one or more objects, each image from a differentviewpoint. For example, the input stage 110 in FIG. 1 depicts an imagewith three Tiki torches.

After the input stage 110, a depth from gradient stage 120 may begin.The depth from gradient stage 120 may include identifying depths foreach point that is an edge of the one or more objects in each image ofthe multiple images. The depths may be generated by locating edges ofthe one or more objects between images, as further described below withreference to FIGS. 2, 4, and 5A-5D.

A filtering stage 130 may be next. In the filtering stage 130, one ormore depths identified in the depth from gradient stage 120 may beremoved. The depths that are removed may be those that are identified asbeing inaccurate based on depths determined in other images. In someembodiments, depths may be removed when they are inconsistent betweendifferent images. For example, a first image may indicate that a firstpoint is a first depth. A second image and a third image may indicatethat a point corresponding to the first point is a second depth, thesecond depth notably different than the first depth. Accordingly, thefirst point may be set as a second depth.

A propagation stage 140 may expand identified depths to areas betweenedges. For example, an edge may be determined to be a silhouette edge ora texture edge. A silhouette edge may be a boundary of an object wherepoints on each side of the texture have different depths, one sidehaving approximately the same depth as the silhouette edge and the otherside having a different depth. For a texture edge, points on both sidesof the edge may have similar trajectories (e.g., depths), whereas forsilhouette edges, one side of the edge may follow the same trajectory.Accordingly, depths may be expanded according to characteristics oftypes of edges.

The stages in FIG. 1 may end with an aggregation stage 150. Theaggregation stage 150 may combine each of the depth maps that weregenerated to create a three-dimensional mesh for the one or more objectscaptures in the multiple images that were received in the input stage110.

FIG. 2 is a simplified flowchart 200 depicting processing performed forgenerating a mesh for an object according to certain embodiments. Theprocessing depicted in FIG. 2 may be implemented in software (e.g.,code, instructions, program) executed by one or more processing units(e.g., processors, cores) of the respective systems, hardware, orcombinations thereof. The software may be stored on a non-transitorystorage medium (e.g., on a memory device). The method presented in FIG.2 and described below is intended to be illustrative and non-limiting.Although FIG. 2 depicts the various processing steps occurring in aparticular sequence or order, this is not intended to be limiting. Incertain embodiments, the steps may be performed in some different orderor some steps may also be performed in parallel.

In the embodiment depicted in FIG. 2, the processing may begin at block210, when a light field associated with one or more objects is received(sometimes referred to as the input stage, as illustrated at 110 in FIG.1). The light field may be represented by multiple images, each imagecapturing the one or more objects from a different viewpoint. Each imagemay also include an associated camera pose (e.g., an orientation of acamera when capturing the image and/or a location relative to otherimages in the light field).

In some embodiments, the light field may be unstructured, meaning thatthe images representing the light field were captured in an unstructuredmanner. For one illustrative example, the unstructured light field maybe captured by a video camera moving around an object (e.g., an HD videocontaining thousands of frames to sample the light field surrounding oneor more objects). In some embodiments, the light field may be generatedusing high spatio-angular sampling such that fine features of objectsbecome more prominent due to increased coherency and redundancy in data.

At block 220, depths may be computed for edges of the one or moreobjects. In some embodiments, depths for all of the edges of the one ormore objects may be computed for each of the multiple images. A depthfor an edge may be computed using gradients of pixels around the edgefrom images with different viewpoints. For example, a gradient directionover multiple images may give a local, linear approximation of thetrajectory of the edge at a viewpoint, from which a depth of the edgemay be computed, as described below with reference to FIGS. 3-5.

FIG. 3 is a simplified flowchart 300 depicting processing performed fordetermining a depth of a point on an object according to certainembodiments. The processing depicted in FIG. 3 may be implemented insoftware (e.g., code, instructions, program) executed by one or moreprocessing units (e.g., processors, cores) of the respective systems,hardware, or combinations thereof. The software may be stored on anon-transitory storage medium (e.g., on a memory device). The methodpresented in FIG. 3 and described below is intended to be illustrativeand non-limiting. Although FIG. 3 depicts the various processing stepsoccurring in a particular sequence or order, this is not intended to belimiting. In certain embodiments, the steps may be performed in adifferent order or some steps may also be performed in parallel. FIG. 4will be used throughout the description of FIG. 3 to further illustratedetermining the depth of the point. FIG. 4 visually depicts determininga depth of first point 414 on an object. FIG. 4 includes first image 410with first optical center 412 and second image 418 with second opticalcenter 420. As can be seen in FIG. 4, the viewpoint of first image 410is different than the viewpoint of second image 418.

In the example depicted in FIG. 3, the processing may begin at 310 whena first point (which corresponds to first point 414 depicted in FIG. 4)of an object is identified in a first image (which corresponds to firstimage 410 depicted in FIG. 4). While not necessary, the first point maybe an edge of the object. To identify an edge of the object, ahigh-gradient region (e.g., large change in color across multiplepixels) of an image may be identified. However, it should be recognizedthat the edge of the object may be identified using other methods. Itshould be recognized that each point (or each edge of the object) in thefirst image may be performed using similar processing described in FIG.3. Referring to FIG. 4, a line 428 from the first optical center 412through the first point 414 may be identified. The line 428 may be usedto estimate a depth of the first point 414. For example, point 415 andpoint 416 illustrate two possible depths that may correspond to thefirst point 414.

At 320, after identifying the first point, an epipolar line (whichcorresponds to epipolar line 422 depicted in FIG. 4) may be identifiedin a second image (which corresponds to second image 418 depicted inFIG. 4). The epipolar line may be for the first point. A person ofordinary skill in the art will recognize that any other suitabletechniques can be used to determine the epipolar line based on the firstpoint. For example, given a calibrations of two cameras, an epipolarline may be computed from a camera matrices. In such an example, a pointin a first image may corresponds to a line in a second image. Thecomputation may use the fundamental matrix between two cameras.

At 330, one or more second points (which include to a second point 423,as depicted in FIG. 4) may be identified along the epipolar line. Theone or more second points may be estimates for a point in the secondimage that corresponds to the first point 414. For example, the epipolarline may be sampled equidistantly to select the one or more secondpoints. The one or more second points may range from a minimum distanceto a camera center to a maximum distance to the camera center. In someexamples, the one or more second points may be used as intersectionpoints for rays (which correspond to rays 424 depicted in FIG. 4) froman optical center of the second image (which corresponds to secondoptical center 420).

At 340, one or more additional points from the first image (whichinclude an additional point 417 depicted in FIG. 4) may be identified.The one or more additional points may be along a line (which correspondto a line 427 depicted in FIG. 4) that intersects the first point (e.g.,the first point 414). In some embodiments, the line that intersects thefirst point may be determined based on the one or more second points.For example, the one or more second points may be projected (sometimesreferred to as back-projected) to the first image using afronto-parallel plane (which corresponds to a fronto-parallel plane 426)placed at a particular depth from the optical center of the first image.In such an example, the one or more additional points may include thefirst point. In some examples, a point (p2) may be selected on a secondline in a second image corresponding to a depth value (d). A plane maybe placed at depth d, which may be parallel to a camera plane of thefirst image. Points may then be projected along the epipolar line aroundp2 to the first image using the plane at depth d. The front-parallelplane may be parallel to a plane of the first image at depth d, wherethe depth is computed using a point on the epipolar line in the secondimage.

At 350, a second point (which corresponds to the second point 423depicted in FIG. 4) of the one or more second points (from the secondimage) is determined to correspond to the first point (which correspondsto the first point 414 depicted in FIG. 4) (from the first image) basedon a color of each of the one or more first points (which correspond tothe points identified on the line 427 depicted in FIG. 4) and a color ofeach of the one or more second points (which correspond to the pointsidentified on the epipolar line 422). The second point may correspond tothe first point when the first point and the one or more additionalpoints have the same or similar color as the one or more second points.For example, the second point may have the same or similar color as thefirst point, and one or more second points around the second point mayhave the same or similar color as one or more first points around thefirst point. A similar color of a first color may refer to a color thatis a different shade but is within a reasonable number of shades of thefirst color.

At 360, a depth for the first point may be computed based on the firstpoint and the second point. For example, the particular depth of thefronto-parallel plane (which may be determined based on the first pointand the second point) used to identify the one or more additional pointsmay be determined to be the depth. The depth of the fronto-parallelplane may or may not be the depth. If both line segments in both imagesare exactly the same, then this depth is the depth. If the line isshifted to one direction, a depth may be computed using the gradientbetween the two line segments, as described below in the next paragraph.

A mathematical description of FIG. 3 will now be described. Given athree-dimensional light field L represented by a set of images (I₁ . . ., I_(n)) (e.g., the first image and the second image), where L(x, y, i)refers to a pixel p=(x, y) (i.e., the first point) in image I_(i) (i.e.,the first image), and their camera projection matrices P_(i), the lightfield gradient ∇L_(i,j) around pixel p (in image I_(i)) and pixel q (inimage I_(j) (i.e., the second image)) may be defined as:

∇L _(i,j)(p,q)=∇s _(i,j)(p,q),

where s_(i,j)(p, q) is a 2×5 image patch constructed by stacking a5-pixel-long light field segment centered at pixel p in image I_(i) anda 5-pixel-long light field segment centered at point q in image I_(j)together. However, it should be recognized that the image patch may be adifferent size. The term s_(i,j)(p, q) may be constructed by using theepipolar geometry between the views image I_(i) and image I_(j): In someexamples, the actual scene point at point p may appear on its epipolarline l in image I_(j).

Given a reference pixel q in image I_(j) along the epipolar line l, amultiple pixel-long segment (e.g., 5-pixel long segment) may be sampledin image I_(j) along the epipolar line l centered at reference pixel qto generate s_(j) (p, q) (i.e., the one or more second points). Thereference pixel q also may correspond to a depth value d_(q) for thepixel p as a result of epipolar geometry. The sampled points may beprojected in image I_(j) back to image I_(i) using a fronto-parallelplane placed at depth d_(q), and sample image I_(i) at these locationsto generate si(p, q) (i.e., the first point and the one or moreadditional points). In some examples, image I_(i) and image I_(j) mayface similar directions. If the depth value d_(q) is the actual depthvalue for pixel p, s_(i)(p, q) and s_(j)(p, q) may be identical. If theactual depth deviates from depth d_(q), the colors in s_(j)(p, q) may bea shifted version of the colors in s_(i)(p, q). In both cases,Vs_(i,j)(p, q) may be used to compute the trajectory of the pointsbetween the two segments using the direction perpendicular to thegradient direction:

γ_(i,j)(p,q)=tan⁻¹(−Λ_(x) s _(i,j)(p,q)/∇_(y) s _(i,j)(p,q)).

Using γ_(i,j)(p, q), we may find the mapping p_(j) ^(s) of pixel p ins_(j)(p, q):

p _(j) ^(s)=1/tan(γ_(i,j)(p,q)),

In some examples, p_(j) ^(s) may be mapped back to epipolar line l tocompute the mapping pj, from which the actual depth d_(p) may becomputed via triangulation, as visually illustrated in FIG. 4.

The next step may be associated with determining how to sample pixel qin image I_(j). If depth d_(q) is close to the actual depth of the scenepoint at pixel p, a reliable depth computation may be expected. However,if the difference between pixel q and p_(j) is larger than a pixel, thegradient computation may become unstable, leading to erroneous results.To that end, epipolar line l may be sampled multiple times betweenq_(min) and q_(max), which correspond to reference points for theminimum and maximum depths of the scene, and get a set of referencepoints q^(k), kϵ1, . . . , K, where K is the number of samples. In someexamples, q^(k) may be sampled one pixel apart from each other, computea mapping p^(k) _(j) for each reference point q^(k), and choose thedepth d^(k) _(p) that maximizes two confidence measures. The colors ofpixel p and p_(j) ^(k) may be expected to be similar due to colorconstancy:

$\left. {{C_{i}^{c}\left( {p,p_{j}^{k}} \right)} = {{\exp \left( {{- \frac{1}{2\sigma_{c}^{2}}}{{{I_{i}(p)} - {I_{j}\left( p_{j}^{k} \right)}}}_{2}^{2}} \right)}.}} \right)$

In some examples, σ_(c) may equal 0.025. The gradient computation mayresult in more robust depth estimates, if q^(k) and p_(j) ^(k) areclose, e.g., the depth d_(p) ^(k) of pixel p is close to the depth ofthe plane d_(p) ^(k) used for gradient computation:

C _(i) ^(d)(p,p _(j) ^(k))=exp(−|d _(q) ^(k) −d _(p) ^(k)|²)

The final confidence measure may be computed by multiplying theindividual components in

C _(i)(p,p _(j) ^(k))=C _(i) ^(c)(p,p _(j) ^(k))·C _(i) ^(d)(p,p _(j)^(k)).

For each pixel p, p_(j) ^(k) may be chosen which maximizes thisconfidence measure as the mapping p_(j), and the depth value d_(p) andthe confidence value C_(p) may be stored.

In some examples, the depth maps may be computed for image I_(i) usingthe nearest neighbors I_(i−1) and I_(i+1), and hierarchically move tonext images in light map L to adjust the depth estimates further. Afterthe initial step, the depth estimate d_(p) for pixel p may be used asthe initial guess, and K reference points q^(k) around the new pixel qin I_(i+2) corresponding to depth d_(p) may be sampled. The referencepoints may again be sampled one pixel apart from each other. In someexamples, as distance increases away from image I_(i) in light map L,the relative motion of a point along the epipolar line with respect tothe change in depth may get faster. However, since we again sample Kreference points, the depth range may be implicitly made smaller at eachstep, leading to more precise depth estimates. Depths may be computedover the views whose viewing directions are no more different from thatof image I_(i) than 5° for each viewpoint, and the final depth mapsD_(i) may be stored with their confidence maps C_(i). Because the scenepoints' trajectories are only visible around high gradient regions, thedepths may be computed only around regions with enough gradientresponse, i.e., ∀p,∥∇I_(i)(p)∥>g, where g=0.05.

FIGS. 5A-5D illustrate an example for determining corresponding pointsof an object (e.g., a basket full of grapes) between images. Forexample, pixels that are determined to be an edge pixel may be selectedfor processing. In some cases, a pixel can be determined to be an edgepixel by calculating a gradient for the pixel. A pixel having a highgradient value can be determined to be an edge pixel. For example, apixel that is adjacent to pixels of a first color in one direction andpixels of a second color in the opposite direction can have a highgradient. A first point 512 (which may correspond to first point 414 inFIG. 4) (sometimes referred to as a pixel) may be selected on an edge ofthe object in a first image 510, as illustrated in FIG. 5A. The firstpoint 512 may be selected because it is on a color edge of the object inthe first image 510.

An epipolar line 522 may be identified in a second image 520, asillustrated in FIG. 5B. The second image 520 may be a differentviewpoint of the object than presented in the first image 510. Theepipolar line 522 may be a function of the position of the first point512 in a three-dimensional space. For example, the epipolar line 522 mayindicate a location of a point in the second image 520 that correspondsto the first point 512.

A second point 524 (sometimes referred to as a pixel) along the epipolarline 522 may be selected from the second image 520, as illustrated inFIG. 5B. The second point 524 may be a first estimate of which point inthe second image 520 corresponds to the first point 512. In some cases,the second point 524 may a point on the epipolar line 522 that is acolor edge, as described above.

After identifying the second point 524, one or more points (sometimesreferred to as one or more second points) may be identified around thesecond point 524. For example, one or more points along the epipolarline 522 on each side of the second point 524 may be identified. Colorvalues (e.g., red, green, and/or blue color components, luma and/orchroma color components, and/or color values of other suitable colorcomponents of the points) of the one or more points may then beextracted, as illustrated in a second row 530 of the grid shown in theimage of FIG. 5C. While FIG. 5C illustrates a particular number ofpoints around the second point 524 used, it should be recognized thatany number of points in each direction may be used, including adifferent number of points in one direction than another direction.

A second line 514 may be identified in the first image 510, asillustrated in FIG. 5A. The second line 514 may correspond to theepipolar line 522. For example, the one or more second points from thesecond image 520 may be projected onto the first image using afronto-parallel plane. Depending on the depth of the fronto-parallelplane, different second lines may be determined. A depth of a plane maybe computed from a “central” point in the epipolar line 522, and thedepth may be used for projection. This may occur multiple times toobtain a best estimate.

After identifying the second line 514, one or more points along thesecond line 514 to each side of the first point 512 may be identified.Color values (e.g., red, green, and/or blue color components, lumaand/or chroma color components, and/or color values of other suitablecolor components of the points) of the one or more points may then beextracted, as illustrated in a first row 528 of the grid shown in theimage of FIG. 5C and as further illustrated in a first row 534 of thegrid shown in the image of FIG. 5D. While FIGS. 5C and 5D illustrateusing a particular number of points around the first point 512, itshould be recognized that any number of points in each direction may beused, including a different number of points in one direction thananother direction.

Colors of points around the first point 512 (e.g., a row of 15 pixels)may also be extracted, as illustrated in a first row 528 in FIG. 5C. Thepoints around the first point 512 may be along the second line 514,which corresponds to the epipolar line 522.

After the first row 528 and the second row 530 of the grid shown in FIG.5C are determined, the rows 528 and 530 may be compared to each other todetermine whether the first point 512 corresponds to the second point524. As illustrated in FIG. 5C by a third line 532, the points in thefirst row 528 and the second row 530 do not line up. Instead, the thirdline 532 illustrates that a point that is two grid boxes to the leftfrom the second point 524 corresponds to the first point 512. In someexamples, the process described above may repeat with the point that istwo points over from the second point 524. By repeating the process, itmay be confirmed that the point that is two points over from the secondpoints 524 corresponds to the first point 512.

While FIG. 5C illustrates the capability to determine which point in thesecond row 530 corresponds to the first point 512, it should berecognized that the determination may just be that the two rows do notmatch, and in such cases a new point must be selected from the epipolarline 522. For example, based on determining that the rows do not match,another point may be newly selected from the second image 520, and theprocess described above may be repeated for the newly selected point. Inone illustrative example depicted in FIG. 5B, a third point 526 alongthe epipolar line 522 may be selected from the second image 520.

After the third point 526 is identified, one or more points (sometimesreferred to as pixels) may be identified around the third point 526. Forexample, one or more points along the epipolar line 522 to each side ofthe third point 526 may be identified. Color values (e.g., red, green,and/or blue color components, luma and/or chroma color components,and/or color values of other suitable color components of the points) ofthe one or more points may then be extracted, as illustrated in a fourthrow 536 of the grid shown in FIG. 5D. While FIG. 5D illustrates using aparticular number of points around the third point 526, it should berecognized that any number of points in each direction may be used,including a different number of points in one direction than anotherdirection.

Similar to as described above, a third row 534 (corresponding to thefirst row 528 in FIG. 5C) and the fourth row 536 may be compared to eachother to determine whether the first point 512 corresponds to the thirdpoint 526. As illustrated in FIG. 5D by a fourth line 538, the points inthe third row 534 and the fourth row 536 do not line up. Instead, thefourth line 538 illustrates that a point that is two points over fromthe third point 526 corresponds to the first point 512. Based ondetermining which points correspond to each other, another point may beselected from the second image 520 to repeat the process describedabove. For example, a fourth point along the epipolar line 522 may beselected from the second image 520, with the fourth point being betweenthe second point 524 and the third point 526. Such an iterative processcan be performed until points are determined to align in rows 528 and530 (or rows 534 and 536), indicating that a matching point has beendetermined. Once a matching point has been determined, a depth for thefirst point 512 may be determined based on the fronto-parallel planeused to determine the points around the first point 512. For example,the front-parallel plane may correspond to a depth, which may be used asthe depth for the first point 512.

Referring back to FIG. 2, at 230, after depths are generated for edgesof the one or more objects for an image, a depth map may be generatedfor the image. The depth map may indicate a depth (e.g., a distance froman optical point) for one or more points in the image. Depth maps may begenerated for each image where depths have been determined.

In some embodiments, a depth map may be compared with other depth mapsto confirm accuracy of the depth map. When a point is identified to beinaccurate (i.e., depths for the points between images do not match),the point may be removed from the depth map based on its inconsistencywith the estimates from other depth maps for other views with similarviewing directions (sometimes referred to as a filtering stage, asillustrated at 130 in FIG. 1).

In some embodiments, the three-dimensional space may be discretizedwhere the foreground object resides using a fine, regular voxel grid(referred to as V). In some examples, the image regions that projectinside this grid may be denoted as foreground pixels, and the rest asbackground pixels.

In order to filter a depth map D_(i) of image I_(i), the depth valuesand the confidences of other views (whose viewing directions are similarto that of image I_(i)) may be back-projected to the voxel grid. In someembodiments, a viewpoint of image I_(i) may be similar to anotherviewpoint of another image when the viewpoint of the other image is nolarger than 15° from the viewpoint of image I_(i). For each vϵV, thecontributions of all back-projected 3D fore-ground points x may besummed using a voting scheme defined as follows:

${{H(v)} = {\sum\limits_{x}^{\;}{c_{x} \cdot {\exp \left( {{- \frac{1}{2\sigma_{c}^{2}}}{{v - x}}_{2}^{2}} \right)}}}},$

where c_(x) is the confidence value associated to x.

The depth D_(i)(p) of each foreground pixel p may be reassigned to thedepth value of the most voted voxel along the viewing ray from thecamera center through pixel p. Because the shape of the foregroundobject may be important, the foreground points may be filtered, whilebackground depths may be kept as they are.

To generate a more complete three-dimensional object reconstruction,depth information may be propagated towards low-gradient regions (e.g.,regions that have not been identified as an edge) (sometimes referred toas a propagation stage, as illustrated at 240 in FIG. 2). Propagationmay be based on whether a high-gradient region (or an edge) correspondsto a texture boundary or an object boundary.

By looking at points around an edge, texture and silhouette edges may bedifferentiated (sometimes referred to as bidirectionalphotoconsistency). A texture edge is a boundary of a pattern wherepoints on both sides of the texture edge have approximately the samedepth. A silhouette edge is a boundary of an object where points on eachside of the texture have different depths, one side having approximatelythe same depth as the silhouette edge and the other side having adifferent depth. For a texture edge, points on both sides of the edgemay have similar trajectories (e.g., depths), whereas for silhouetteedges, one side of the edge may follow the same trajectory.

FIG. 6 illustrates a process 600 for identifying a type of an edge of anobject. The processing depicted in FIG. 6 may be implemented in software(e.g., code, instructions, program) executed by one or more processingunits (e.g., processors, cores) of the respective systems, hardware, orcombinations thereof. The software may be stored on a non-transitorystorage medium (e.g., on a memory device). The method presented in FIG.6 and described below is intended to be illustrative and non-limiting.Although FIG. 6 depicts the various processing steps occurring in aparticular sequence or order, this is not intended to be limiting. Incertain embodiments, the steps may be performed in some different orderor some steps may also be performed in parallel.

In the embodiment depicted in FIG. 6, the processing may begin at 610when an edge of an object is identified in a first image. While only oneedge is referred to here, it should be recognized that this process maybe repeated for each edge of the object.

At 620, a first line in the first image may be identified. The firstline may be perpendicular to the edge in the first image. For example,if the edge is going from top to bottom of the first image, the firstline may be going from left to right of the first image. At 630, aplurality of points around the edge in the first image may beidentified. The plurality of points may be along the first line. Forexample, one or more points on a first side of the edge in the firstimage may be identified and one or more points on a second side of theedge in the first image may also be identified.

At 640, the edge of the object in a second image may be identified. Thesecond image may be from a similar viewpoint as the first image. Incertain embodiments, two images are from a similar viewpoint when aviewpoint of the first image is less than 15 degrees different from aviewpoint of the second image. The edge may be identified by embodimentsdescribed above.

At 650, a second line in the second image may be identified. The secondline may be perpendicular to the edge in the second image, similar to asdescribed above. At 660, a plurality of second points around the edge inthe second image may be identified. The plurality of second points maybe along the second line. For example, one or more points on a firstside of the edge in the second image may be identified and one or morepoints on a second side of the edge in the second image may also beidentified.

At 670, a type of the edge may be identified based on a color of each ofone or more points of the plurality of first points and a color of eachof one or more points of the plurality of second points. The type of theedge may be identified as either a silhouette edge or a texture edge. Asilhouette edge may be an edge that includes pixels associated with anobject on both sides of the edge. A texture edge may be an edge thatincludes pixels associated with an object only on one side of the edge.

FIG. 7 illustrates an example of an image 700 where edges may beidentified. In the image 700, there are two objects: a first object 710and a second object 720. As can be seen from the image 700, it may bedifficult to determine which edges are parts of an object and whichedges indicate a transition from an object to another object.

Windows 712 and 722 depict zoomed in areas of the first object 710 andthe second object 720. Window 712 provides examples of silhouette edges,and window 722 provides examples of texture edges. The silhouette edgesin window 712 are included in a leg of the first object 710. The textureedges in window 722 are included on skin of the second object 720.

To determine that an edge in the window 712 is a silhouette edge, afirst line 714 may be identified in image 700. The first line 714 may beperpendicular to an edge identified in the window 712. The first line714, as described above, may be used to identify pixels to use whendetermining a type of the edge.

Similarly, to determine that an edge in the window 722 is a textureedge, a second line 724 may be identified in image 700. The second line724 may be perpendicular to an edge identified in the window 722. Thesecond line 724, as described above, may be used to identify pixels touse when determining a type of the edge.

While FIG. 7 only illustrates a single image, it should be recognizedthat there may be several images of the first object 710 and/or thesecond object 720 that are each taken from a different viewpoint. Ineach of the different viewpoints (where the viewpoints are similar tothe viewpoint depicted in FIG. 7), a second edge corresponding to theedge may be identified. The second edge may be identified by processesdescribed above. And for each of the second edges, points may bedetermined using lines similar to as described above. Then, color values(e.g., red, green, and/or blue color components, luma and/or chromacolor components, and/or color values of other suitable color componentsof the points) of points from each image may be compared to each other,as depicted in FIGS. 8A and 8B.

FIG. 8A illustrates an example of points for a first edge from multipleimages. In the example, each row may be a different image. For example,a first row 814 may be from a first image, where each column correspondsto a different point in the first image. Accordingly, FIG. 8A isillustrating an example with 15 different images and two points fromeach side of the point.

When determining a type of the edge, it can be determined whethercorresponding points between images have similar colors. If thecorresponding points between images do have similar colors, it may beassumed that the edge is a texture edge. This is because the differentviewpoints will effectively go around the object. While a silhouetteedge would not be consistent when going around because of changes inbackground, a texture edge would be consistent when going around.Accordingly, the edge may be determined as a silhouette edge when thepoints on a particular side of the edge are not consistent across theimages (e.g., some images have the points as a first color and someimages have the points as a second color). The determination for theedge is confirmed by identifying that points left of the edge areprimarily a single color.

Similarly as described above, FIG. 8B illustrates an example of pointsfor a second edge from multiple images. In the example, each row may bea different image. For example, a first row 822 may be from a firstimage, where each column corresponds to a different point in the firstimage. Accordingly, FIG. 8A is illustrating an example with 15 differentimages and two points from each side of the point.

When determining a type of the edge, it can be determined whethercorresponding points between images have similar colors. If thecorresponding points between images do have similar colors, it may beassumed that the edge is a texture edge. This is because the differentviewpoints will effectively go around the object. While a backgroundpoint would not be consistent when going around the edge, a texture edgewould have similar points when going around the edge. Accordingly, theedge may be determined as a texture edge because the points left andright of the edge are relatively consistent across the images (e.g., allcorresponding points across the images have relatively the same color).

FIGS. 9A and 9B illustrate results of identifying edges in an image. Forexample, FIG. 9A illustrates edges that may be identified as silhouetteedges, and FIG. 9B illustrates edges that may be identified as textureedges. And when an area is completely enclosed by texture edges, eachpoint in the area may be assigned a depth based on the texture edges.

Embodiments described above regarding determining a type of an edge willnow be described mathematically. In particular, a texture variation maybe measured on both sides of an edge separately. For a pixel p in I_(i),whose depth value is d_(p)=D_(i)(p), its image gradient direction may befirst computed:

θ(p)=tan⁻¹(∇_(y) I _(i)(p)/∇_(x) I _(i)(p)).

Note that θ(p) may be different than γ_(i,j)(p, q); θ(p) may be computedper image, whereas γ_(i,j)(p, q) may be computed between differentimages inside L. Then, a thin rectangular patch on each side of pixel palong θ(p) may be sampled. In some examples, the sampled pixels may bevectorized within the two patches, and the one taken in the positiveθ(p) direction may be denoted by f₊ and the other by f⁻. The two patchesmay then be projected to the neighboring views in light field L througha fronto-parallel plane placed at depth d_(p). In a second view, sayimage I_(j), the pixels within the projected patches may be sampled,forming g₊ and g⁻, also vectorized. In certain embodiments, for eachdirection, three pixels along θ(p) in image I_(i) (i.e., a first image)and three other pixels in image I_(j) (i.e., a second image) may besampled at the locations that are projected from the three pixels ofimage I_(i). One side of the photoconsistency for pixel p between imageI_(i) and image I_(j) may then be defined as the patch differencebetween f₊ and g₊:

$\left. {{p\left( {f_{+},g_{+}} \right)} = {{\exp \left( {{- \frac{1}{2\sigma_{p}^{2}}}{{f_{+} - g_{+}}}_{2}^{2}} \right)}.}} \right)$

The other side of the photoconsistency may be defined similarly for f⁻and g⁻. In some examples, σ_(p) may be chosen to be the same as σ_(c)above. The bidirectional photoconsistency values C₊(p) and C⁻(p) may becomputed by averaging all pairwise photo-consistency values among theviews in light field L whose viewing directions are below a threshold(e.g., no more different than 5° from that of image I_(i)).

The bidirectional photoconsistency may indicate the likelihood of bothsides being on the same depth as pixel p: if pixel p is on thesilhouette, the background seen in one side will move at a differentspeed with respect to the camera, leading to a low consistency value forthat side. The differentiation between texture and silhouette edges mayhelp decide on the direction to which the depth is propagated.

The depth maps D_(i) may be sparsely sampled because the depths and theconsistencies may be computed only on high gradient regions. In thisstep, the depths and the consistencies may be propagated to smoothregions using edge-aware filtering, thereby exploiting the computedphotoconsistencies. However, each pixel p on a high gradient region mayhave two photoconsistency values, one for each direction along θ(p),which may require special care during filtering. Because the directneighbors in these directions should share the depth and confidencevalues with the edge regions, a simple splatting strategy may be used toavoid this special case: The neighboring pixel p′ in the positive θ(p)direction from p may be assigned C₊(p), whereas the neighboring pixel inthe negative θ(p) direction may be assigned C⁻(p). The depth valuesD_(i)(p′) with D_(i)(p) may be initialized. If a pixel p′ may beaffected by multiple pixels on high gradient regions, the depth andconfidence values from the neighbor may be chosen with the highestconfidence value. For the high gradient regions, the higher value ofC₊(p) and C⁻(p) may be kept as C_(i)(p).

Now that per-pixel depth and confidence maps may be computed for eachview, confidence-weighted joint-edge-aware filtering may be employedusing the images I_(i) inside light field L as the joint-domains, whichmay make use of a geodesic filter. First, D_(i) and C_(i) may bemultiplied element-wise and D_(i) and C_(i) may be filtered using thegeodesic filter with I_(i) as the joint domain, which generates (C_(i) ⊙D_(i))′, where ⊙ represents element-wise multiplication. This processmay give higher emphasis to depth values with higher confidence. Theresults may then be normalized by dividing (C_(i) ⊙ D_(i))′ by C_(i)′,the filtered version of the confidence map, again element-wise. Thefinal depth map may be computed as

$D_{i}^{\prime} = {\left( \frac{\left( {C_{i}\bullet \; D_{i}} \right)^{\prime}}{C_{i}^{\prime}} \right).}$

In order to avoid depth values that are vaguely between the foregroundobject and the background clutter, the filtering operation may beapplied for the foreground and background depth maps separately. If theconfidence at pixel p is larger in the foreground depth map, this depthvalue may be kept for that pixel, and vice versa. The final confidencemap may then be the absolute difference between the confidence maps forthe foreground and background depth maps. From this point on, D, and C,will be referred to as D_(i) and C_(i), respectively.

The depth propagation step may generate dense depth maps for each inputimage I_(i) independently, where smooth regions are assigned depthvalues by interpolating known depth values at image edges. These depthmaps may already describe the objects shape as a point cloud, but mayhave inconsistencies due to the inexact image-space filtering operation.

Referring back to FIG. 2, at 240, the depth maps may be aggregated in athree-dimensional space (sometimes referred to as an aggregation stage,as illustrated at 150 in FIG. 1). The aggregation may reconstruct aglobally consistent object representation in the form of a mesh (asdescribed at 150 in FIG. 1, where a mesh for the object is generatedbased on the aggregated depth maps).

Because the number of views may be in the order of thousands, computingglobally consistent depth maps might not be a viable option due to thetime complexity. On the other hand, having a very large number of depthmaps may have the advantage that their consensus in three-dimensionalspace provides enough information to infer the actual surface. Noisyestimates from a small number of views may be tolerated by correctestimates from other views that see the same scene point.

The same voxel grid V as described above may be used, but this time,both foreground and background points may be utilized. For each vϵV, theprobability H(ν) of that voxel being on the surface of the object may becomputed. In order to compute these probabilities, every voxel v may beprojected to the images, and D_(i) and C_(i) may be interpolated. Givena voxel v projects to a subpixel location p_(i) in image I_(i), withinterpolated depth value d_(i) and confidence value c_(i), the per-viewprobability of having the surface at v may be computed bydifferentiating between two cases. If depth d_(i) falls inside V, it maybe a foreground point. The confidence c_(v,i) of having the surface at vmay be computed using an exponential decay function, depending on thedifference between d_(i) and d_(ν,i), the depth of v with respect toimage I_(i):

c _(ν,i) =c _(i)·exp(−|d _(i) −d _(ν,i)|₂ ²/(2σ_(ν) ²)).

If depth d_(i) is outside V, i.e., is a background point, thenc_(ν,i)=−c_(i), because all voxels on this viewing ray should be in freespace and affected in the same magnitude. Using these confidence values,Bayes' rule may be directly applied to compute the per-view probabilityP_(i)(νϵS|c_(v,i)) of having the surface at v, given the confidencevalue:

${P_{i}\left( {{v \in S}c_{v,i}} \right)} = \frac{{P\left( {c_{v,i}{v \in S}} \right)} \cdot {P\left( {v \in S} \right)}}{P\left( c_{v,i} \right)}$

where S stands for the set of voxels on the object surface. In someexample P(c_(ν),i|νϵS) may be modeled, e.g., the confidence value of asurface voxel v, using N(1, σ_(s)), with a normal distribution with meanof 1, to handle noise of per-view depth maps. The confidence value of avoxel in the free space, denoted by P(c_(ν,i)|νϵF), may also be modeledwith a normal distribution N(−1,σ_(s)), but with mean of −1. Thedenominator in the equation above may be computed as follows:

P(c _(ν,i))=P(c _(ν,i) |νϵS)·P(vϵS)+

+P(c _(ν,i) |νϵF)·P(νϵF).

In some examples, P(νϵF) and P(νϵS) may be modeled to be of equalprobability, 0.5, due to no prior knowledge about the scene.

In some examples, the aggregation scheme may accumulate the per-imageprobabilities using a geometric mean. Given all P_(i)(νϵS|c_(ν,i)), theprobability H(v) may be computed using the following formula:

${H(v)}{\left( {\prod\limits_{i - 1}^{n}\; {P_{i}\left( {{v \in S}c_{v,i}} \right)}} \right)^{1/n}.}$

The surface may be generated by thresholding H(v) at 0.2 and applyingmarching cubes. In some examples, a small value may be used forthresholding, because the surface probabilities may be generally ofsmaller magnitude compared to the free space probabilities.

In some examples, the resulting mesh may already capture most details ofthe object and may be ready to be used as is. In order to pronounce thefine details further, the photoconsistency of the voxels inside thesurface may be examined.

A general solution for refining the mesh may be to apply volumetricgraph-cuts inside the voxel grid. However, untextured thin features,like the legs and arms in the AFRICA dataset, or the straw details ofthe BASKET dataset, pose a problem for graph-cuts. Around such features,photoconsistency measures might not clearly point to the objectboundary, and the graph-cut result may remove them from the finalreconstruction altogether. Instead, a voxel carving approach may beused, which only carves out inconsistent voxels and keeps the thinfeatures intact.

In some examples, a region of interest R inside the mesh may becomputed, which is 3 voxels deep from the surface, and mesh normalsinside R may be propagated. The visibility of the voxels may be computedusing the current mesh as a prior and rendering the back-facing facesfrom each view point I_(i). If a voxel's depth is smaller than the depthof the mesh seen from I_(i), then it may be counted as visible fromimage I_(i). After all voxels vϵR are projected to all images I_(i),given a voxel ν, the color values {c_(v)(i)} and the weights {w_(v)(i)}may be gathered from all images I_(i) to which it projects. The weightsof views that are not seeing the voxel may be set to 0. For all otherviews, the weight may be computed as the dot product of the voxel normaln_(ν) and the viewing ray from I_(i) to v, namely r_(v,i):

${w_{v}(i)} = \left\{ \begin{matrix}{n_{v} \cdot r_{v,i}} & {{{if}{\mspace{11mu} \;}{n_{v} \cdot r_{v,i}}} > 0} \\{0,} & {otherwise}\end{matrix} \right.$

Given the colors and weights, a weighted variance of the colors may becomputed as the photoconsistency PC(ν):

${{{PC}(v)} = {\sum\limits_{i = 1}^{n}{{w_{v}(i)}{\left( {{c_{v}(i)} - \mu_{v}} \right)^{2}/{\sum\limits_{i = 1}^{n}{w_{v}(i)}}}}}},$

where μ_(v) is the weighted average of c_(v). In some examples, allvoxels that have PC(ν) lower than a threshold, which we set to 0.95, maybe carved out. The carving may be repeated until no voxels are carvedout. The voxel carving approach may be very efficient in removingunnecessary voxels from the surface, and may converge very quickly.Finally, all voxels v and their normals n_(ν) on the boundary of R maybe supplied to a Poisson surface reconstruction to generate a finalresult.

Embodiments of the description above may be depicted by simplifiedflowcharts. For example, FIG. 10 is a simplified flowchart 1000depicting processing performed for object reconstruction using aparticular depth detection technique. The processing depicted in FIG. 10may be implemented in software (e.g., code, instructions, program)executed by one or more processing units (e.g., processors, cores) ofthe respective systems, hardware, or combinations thereof. The softwaremay be stored on a non-transitory storage medium (e.g., on a memorydevice). The method presented in FIG. 10 and described below is intendedto be illustrative and non-limiting. Although FIG. 10 depicts thevarious processing steps occurring in a particular sequence or order,this is not intended to be limiting. In certain embodiments, the stepsmay be performed in a different order or some steps may also beperformed in parallel.

In the example depicted in FIG. 10, the processing may begin at 1010when a light field represented by a plurality of images of an object isreceived. The plurality of images may include a first image and a secondimage, where the second image is at a viewpoint different than butsimilar to the first image. In some embodiments, the light field may beunstructured.

At 1020, a first point of the object may be identified in the firstimage. The first point may be identified based on the first point beingan edge of the object, as described above.

At 1030, a second line may be identified in the second image based onthe first point in the first image. The second line may be an epipolarline, as described above. In some embodiments, the second line may havea direction of an epipolar line for the first point in the first image.At 1040, one or more second points may be identified along the secondline. The one or more second points may be consecutive points along thesecond line.

At 1050, one or more first points may be identified along a first lineintersecting the first point. Each point of the one or more first pointsmay be projected from the one or more second points.

At 1060, it may be determined that a second point of the one or moresecond points corresponds to the first point based on a color of each ofthe one or more first points and a color of each of the one or moresecond points.

At 1070, a depth may be computed for the first point based on the firstpoint and the second point. The depth may be computed in response todetermining that the second point corresponds to the first point. Insome embodiments, a color gradient is used to compute the depth. Thecolor gradient may be computed using colors of the one or more firstpoints and the one or more second points.

At 1080, a depth map may be generated for the first image using thedepth of the first point. At 1090, a mesh may be generated for theobject based on the depth map.

FIG. 11 is a simplified flowchart 1100 depicting processing performedfor object reconstruction using a particular propagation technique. Theprocessing depicted in FIG. 11 may be implemented in software (e.g.,code, instructions, program) executed by one or more processing units(e.g., processors, cores) of the respective systems, hardware, orcombinations thereof. The software may be stored on a non-transitorystorage medium (e.g., on a memory device). The method presented in FIG.11 and described below is intended to be illustrative and non-limiting.Although FIG. 11 depicts the various processing steps occurring in aparticular sequence or order, this is not intended to be limiting. Incertain embodiments, the steps may be performed in a different order orsome steps may also be performed in parallel.

In the example depicted in FIG. 11, the processing may begin at 1110when a light field represented by a plurality of images is received.Each image of the plurality of images may be at a different viewpoint,where the plurality of images are associated with an object.

At 1120, a depth may be determined for a color edge of the object in animage of the plurality of images. At 1130, the depth for the color edgemay be propagated to one or more points around the color edge based on atype of the color edge. The depth for the color edge may be propagatedin two directions when the color edge is determined to be a texture. Thedepth for the color edge may be propagated in a single direction whenthe color edge is determined to be a silhouette.

At 1140, a depth map may be generated for the image using the depth forthe color edge and the depth for the one or more points. At 1150, a meshmay be generated for the object based on the depth map. In someembodiments, the depth map may be a first depth map. In suchembodiments, the mesh may be generated by aggregating the first depthmap with a second depth map, where the second depth map is for anadditional image of the plurality of images.

In some embodiments, the process depicted in FIG. 11 may further includeidentifying a plurality of points along a first line perpendicular tothe color edge in the image. The processing may further includeidentifying a second image of the plurality of images, where the secondimage is a similar viewpoint as the image. The processing may furtherinclude identifying the color edge in the second image, identifying aplurality of points along a second line perpendicular to the color edgein the second image, and determining the type of the color edge based ona color of each of the one or more points along the first line and eachof the one or more points along the second line. In some embodiments,the plurality of points along the first line may be a first imagegradient and the plurality of points along the second line may be asecond image gradient. In some embodiments, a first point of theplurality of points along the first line is on a particular side of thecolor edge in the first image and a second point of the plurality ofpoints along the second line is on the particular side of the color edgein the second image. The color edge may be a first type when the firstpoint and the second point are different colors. The color edge may be asecond type when the first point and second point are the same color.

FIG. 12 illustrates a schematic diagram of an example of a computersystem 1200. This system is exemplary only and one having skill in theart will recognize that variations and modifications are possible. Thecomputer system 1200 can be used for the operations described above. Forexample, the computer system 1200 shown in FIG. 12 may be used toimplement any or the entire tracking framework (e.g., training andtracking stage) techniques and routines described herein.

The system 1200 includes a processor 1210, a memory 1220, a storagedevice 1230, and an input/output interface 1240. Each of the components1210, 1220, 1230, and 1240 are interconnected using a system bus 1250.The processor 1210 is capable of processing instructions for executionwithin the computer system 1200. In one implementation, the processor1210 is a single-threaded processor. In another implementation, theprocessor 1210 is a multi-threaded processor. The processor 1210 iscapable of processing instructions stored in the memory 1220 or on thestorage device 1230 to provide graphical information via input/outputinterface 1240 for display on a user interface of one or moreinput/output device 1260.

The memory 1220 stores information within the computer system 1200 andmay be associated with various characteristics and implementations. Forexample, the memory 1220 may include various types of computer-readablemedium such as volatile memory, a non-volatile memory and other types ofmemory technology, individually or in combination.

The storage device 1230 is capable of providing mass storage for thecomputer system 1200. In one implementation, the storage device 1230 isa computer-readable medium. In various different implementations, thestorage device 1230 may be a floppy disk device, a hard disk device, anoptical disk device, or a tape device.

The input/output device 1260 provides input/output operations for thecomputer system 1200. In one implementation, the input/output device1260 includes a keyboard and/or pointing device. In anotherimplementation, the input/output device 1260 includes a display unit fordisplaying graphical user interfaces.

The features described can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The apparatus can be implemented in a computerprogram product tangibly embodied in an information carrier, e.g., in amachine-readable storage device, for execution by a programmableprocessor; and method steps can be performed by a programmable processorexecuting a program of instructions to perform functions of thedescribed implementations by operating on input data and generatingoutput. The described features can be implemented advantageously in oneor more computer programs that are executable on a programmable systemincluding at least one programmable processor coupled to receive dataand instructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. A computer program is a set of instructions that can be used,directly or indirectly, in a computer to perform a certain activity orbring about a certain result. A computer program can be written in anyform of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors ofany kind of computer. Generally, a processor will receive instructionsand data from a read-only memory or a random access memory or both. Theessential elements of a computer are a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer will also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,ASICs (application-specific integrated circuits).

To provide for interaction with a user, the features can be implementedon a computer having a display device such as a CRT (cathode ray tube),LCD (liquid crystal display), LED (light emitting diode) monitor fordisplaying information to the user and a keyboard and a pointing devicesuch as a mouse or a trackball by which the user can provide input tothe computer.

The features can be implemented in a computer system that includes aback-end component, such as a data server, or that includes a middlewarecomponent, such as an application server or an Internet server, or thatincludes a front-end component, such as a client computer having agraphical user interface or an Internet browser, or any combination ofthem. The components of the system can be connected by any form ormedium of digital data communication such as a communication network.Examples of communication networks include a LAN, a WAN, and thecomputers and networks forming the Internet.

The computer system can include clients and servers. A client and serverare generally remote from each other and typically interact through anetwork, such as the described one. The relationship of client andserver arises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.Although a few implementations have been described in detail above,other modifications are possible.

In addition, the logic flows depicted in the figures do not require theparticular order shown, or sequential order, to achieve desirableresults. In addition, other steps may be provided, or steps may beeliminated, from the described flows, and other components may be addedto, or removed from, the described systems. Accordingly, otherimplementations are within the scope of the following claims.

Where components are described as being configured to perform certainoperations, such configuration can be accomplished, for example, bydesigning electronic circuits or other hardware to perform theoperation, by programming programmable electronic circuits (e.g.,microprocessors, or other suitable electronic circuits) to perform theoperation, or any combination thereof.

A number of embodiments of the present disclosure have been described.Nevertheless, it will be understood that various modification may bemade without departing from the scope of the present disclosure.

What is claimed is:
 1. A method for object reconstruction, the methodcomprising: receiving a light field represented by a plurality of imagesof an object, wherein the plurality of images include a first image anda second image, and wherein the second image is at a viewpoint differentthan the first image; identifying a first point of the object in thefirst image; identifying a second line in the second image based on thefirst point in the first image; identifying one or more second pointsalong the second line; identifying one or more first points along afirst line intersecting the first point, wherein each point of the oneor more first points is projected from the one or more second points;determining that a second point of the one or more second pointscorresponds to the first point based on a color of each of the one ormore first points and a color of each of the one or more second points;computing a depth for the first point based on the first point and thesecond point, wherein the depth is computed in response to determiningthat the second point corresponds to the first point; generating a depthmap for the first image using the depth of the first point; andgenerating a mesh for the object based on the depth map.
 2. The methodof claim 1, wherein the second line has a direction of an epipolar linefor the first image.
 3. The method of claim 1, wherein the second pointis an estimate of where the first point is in the second image.
 4. Themethod of claim 1, wherein a color gradient is computed using colors ofthe one or more first points and the one or more second points, andwherein the color gradient is used to compute the depth.
 5. The methodof claim 1, wherein the first point is a color edge of the object, andwherein the second point corresponds to the first point such that thesecond point is the color edge of the object.
 6. The method of claim 1,wherein the light field is unstructured.
 7. The method of claim 1,wherein a viewpoint of the first image is similar to a viewpoint of thesecond image.
 8. A non-transitory computer-readable storage mediumstoring a plurality of instructions executable by one or moreprocessors, the plurality of instructions when executed by the one ormore processors cause the one or more processors to: receive a lightfield represented by a plurality of images of an object, wherein theplurality of images include a first image and a second image, andwherein the second image is at a viewpoint different than the firstimage; identify a first point of the object in the first image; identifya second line in the second image based on the first point in the firstimage; identify one or more second points along the second line;identify one or more first points along a first line intersecting thefirst point, wherein each point of the one or more first points isprojected from the one or more second points; determine that a secondpoint of the one or more second points corresponds to the first pointbased on a color of each of the one or more first points and a color ofeach of the one or more second points; compute a depth for the firstpoint based on the first point and the second point, wherein the depthis computed in response to determining that the second point correspondsto the first point; generate a depth map for the first image using thedepth of the first point; and generate a mesh for the object based onthe depth map.
 9. The non-transitory computer-readable storage medium ofclaim 8, wherein the second line has a direction of an epipolar line forthe first image.
 10. The non-transitory computer-readable storage mediumof claim 8, wherein the second point is an estimate of where the firstpoint is in the second image.
 11. The non-transitory computer-readablestorage medium of claim 8, wherein a color gradient is computed usingcolors of the one or more first points and the one or more secondpoints, and wherein the color gradient is used to compute the depth. 12.The non-transitory computer-readable storage medium of claim 8, whereinthe first point is a color edge of the object, and wherein the secondpoint corresponds to the first point such that the second point is thecolor edge of the object.
 13. The non-transitory computer-readablestorage medium of claim 8, wherein the light field is unstructured. 14.The non-transitory computer-readable storage medium of claim 8, whereina viewpoint of the first image is similar to a viewpoint of the secondimage.
 15. A system comprising: one or more processors; and anon-transitory computer-readable medium including instructions that,when executed by the one or more processors, cause the one or moreprocessors to: receive a light field represented by a plurality ofimages of an object, wherein the plurality of images include a firstimage and a second image, and wherein the second image is at a viewpointdifferent than the first image; identify a first point of the object inthe first image; identify a second line in the second image based on thefirst point in the first image; identify one or more second points alongthe second line; identify one or more first points along a first lineintersecting the first point, wherein each point of the one or morefirst points is projected from the one or more second points; determinethat a second point of the one or more second points corresponds to thefirst point based on a color of each of the one or more first points anda color of each of the one or more second points; compute a depth forthe first point based on the first point and the second point, whereinthe depth is computed in response to determining that the second pointcorresponds to the first point; generate a depth map for the first imageusing the depth of the first point; and generate a mesh for the objectbased on the depth map.
 16. The system of claim 15, wherein the secondline has a direction of an epipolar line for the first image.
 17. Thesystem of claim 15, wherein the second point is an estimate of where thefirst point is in the second image.
 18. The system of claim 15, whereina color gradient is computed using colors of the one or more firstpoints and the one or more second points, and wherein the color gradientis used to compute the depth.
 19. The system of claim 15, wherein thefirst point is a color edge of the object, and wherein the second pointcorresponds to the first point such that the second point is the coloredge of the object.
 20. The system of claim 15, wherein the light fieldis unstructured.